In piston-and-cylinder-type internal combustion engines, whether Otto or diesel engines, each cylinder is, for reasons of combustion technology, associated with two intake valves and two exhaust valves. The intake valves, on the one hand, and the exhaust valves, on the other hand, are actuated simultaneously corresponding to the operational cycle of the engine. Particularly in diesel engines the cylinder head also has to accommodate an injection device.
In engines having a camshaft disposed at a level under the cylinder head, in which case the valve actuation is effected by push rods and rocker arms, few positional problems, if any are encountered because above the valves sufficient free space can be reserved for the required additional aggregates as it is described, for example, in German Offenlegungsschriften (applications published before examination) 12 98 103, 14 51 949, 15 76 267 and 19 06 882.
In a more compact construction as required particularly in personal automotive vehicles, the camshaft has been relocated to extend at a level above the valves in the zone of the cylinder head and the valves which are to be simultaneously actuated are connected with a coupling mechanism so that the valves to be actuated simultaneously can be operated by a single cam. Such an arrangement is disclosed, for example, in Published European Applications 0 144 179, 0 503 145 and 0 570 963. The prior art constructions disclosed therein, however, generally make it necessary to provide separate camshafts for the operation of the intake valves, on the one hand and for the operation of the exhaust valves, on the other hand. Published European Patent Application 0 144 179, in addition to the arrangement of two overhead camshafts (FIG. 2) proposes an embodiment having a sole overhead camshaft (FIG. 4). In the latter case, the construction is such that each valve is associated with its own rocker arm which involves a significantly complex construction. Furthermore, the last-outlined arrangement is not adapted for fuel-injected engines, particularly diesel engines, because no required free space is available for accommodating the injection device which is to be placed between the valve openings.
Published European Patent Application 0 504 128 describes a cylinder head for an internal combustion engine in which the simultaneously operated valves are actuated by a single camshaft by means of differently oriented cams. The valves to be operated simultaneously are connected with one another by a valve bridge which is engaged by one end of a rocker arm while its other end contacts the associated cam of the camshaft by a follower roller. In such an arrangement, however, the camshaft is situated laterally adjacent the cylinder outline defined by the cylinder head bolts so that a disassembly of the cylinder head is possible only after removal of the valve drive.